UNIVERSITY   OF    CALIFORNIA 

COLLEGE   OF    AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 

CIRCULAR  No.  289 

May,  1925 

OAK  FUNGUS  IN  ORCHARD  TREES 


BY 

A.  H.  HENDEICKSON' 


^^ 


Oak  fungus  (Armillaria  mellea)  is  a  root  disease  of  widespread 
economic  importance  in  California.  It  attacks  most  of  the  common 
deciduous  fruit  trees  and  is  also  found  on  many  other  plants  including 
annuals  and  perennials.  As  its  common  name  indicates,  the  native 
oak  trees  are  generally  considered  the  source  of  infection.  The  disease 
spreads  underground  and  often  kills  orchard  trees  over  a  considerable 
area.  Trees  replanted  in  infected  orchards  from  which  diseased  trees 
have  been  removed  usually  die  within  a  few  years  unless  resistant 
species  are  used. 

APPEARANCE  AND  BEHAVIOE 

The  characteristic  behavior  of  trees  infected  with  this  disease  makes 
it  comparatively  easy  to  identify  the  fungus.  Diseased  trees  may  die 
at  any  time  during  the  year.  Their  roots  show  flat  white  fan-shaped 
mycelium  (a  thin  felted  sheet  of  fungous  threads)  between  the  bark 
and  the  wood.  This  mycelium  is  usually  confined  to  the  roots,  and  only 
in  exceptional  cases  does  it  extend  into  the  trunk  above  ground.  The 
odor  of  a  freshly  dug  root  from  a  diseased  tree  is  distinctive  and  is 
described  by  W.  T.  Home  as  having  a  ''sharp,  rather  agreeable  mush- 
room smell."  The  presence  of  the  flat  white  mycelium  and  peculiar 
mushroom  odor  serves  as  an  excellent  means  of  identifying  this  disease. 
Roots  of  fruit  trees  attacked  by  it  decay  rather  quickly.  The  advanc- 
ing edge  of  the  fungus  is  usually  shown  by  a  darkening  of  the  wood. 

Slender  brown  or  purple  thread-like  cords  are  sometimes  found 
on  the  surface  of  the  roots.  These  root-like  organs  are  the  rhizomorphs 
by  which  the  fungus  spreads  underground  from  tree  to  tree.  It  is 
believed  that  the  rhizomorphs  are  the  principal  means  of  spreading  the 
disease.  They  are  not  always  present  in  abundance  on  fruit  tree  roots 
and  are  often  passed  unnoticed.    Whenever  one  of  these  rhizomorphs 

*  Assistant  Professor  of  Pomology,  University  of  California. 


Z  UNIVERSITY    OF    CALIFORNIA^ EXPERIMENT    STATION 

comes  in  contact  with  a  tree  root,  it  quickly  enters  and  in  time  infects 
the  entire  root  system. 

During  the  rainy  season  clumps  of  toadstool  sporophores  often 
appear  near  the  crown  of  the  diseased  trees.  These  toadstools  are  of 
a  light  tan  color  on  the  top,  usually  showing  light  brown  scales.  The 
loAver  surface  is  white  and  is  made  up  of  fine  delicate  structures  known 
as  gills,  which  bear  the  spores  or  reproductive  bodies.  The  size  of 
these  clumps  varies  considerably.  They  may  consist  of  comparatively 
few  toadstools,  or  they  may  be  as  much  as  two  feet  in  diameter.  The 
spores,  which  are  produced  in  great  numbers,  apparently  do  not  attack 
living  plants,  and  hence  there  is  nothing  to  be  gained  by  destroying  the 
toadstools.  Ordinarily,  the  whole  clump  turns  dark  within  a  few 
days,  becomes  infested  with  the  larvae  of  certain  fungous  gnats,  and 
melts  down  to  a  slimy  mass.  While  the  spores  are  not  thought  to  be 
important  in  disseminating  the  disease,  the  presence  of  one  of  these 
clumps  indicates  that  the  fungus  is  established  in  the  tree  and  that 
the  tree  is  doomed  to  die  within  a  comparatively  short  time.  Usually, 
the  whole  tree  dies  suddenly  (fig.  1)  but  occasionally  one  side  may 
die  and  leave  the  remainder  apparently  healthy.  This  condition  seems 
due  to  the  fact  that  the  roots  on  one  side  are  killed  before  the  disease 
has  become  established  throughout  the  root  system.  The  remainder  of 
the  tree  generally  dies  within  a  year  or  two.  When  a  fruit  tree  has 
once  become  infected,  it  is  inevitably  killed.  After  the  disease  reaches 
the  crown,  treatments  with  disinfectants  or  by  surgery  have  not  proved 
effective.  There  are  but  few,  if  any,  authentic  cases  where  an  infected 
tree  has  survived  more  than  one  or  two  seasons  after  treatment. 

One  of  the  chief  characteristics  of  the  disease  is  its  manner  of 
spreading.  From  the  original  source  of  infection,  the  disease  spreads 
outward  from  tree  to  tree  in  all  directions.  The  infected  area  is 
irregularly  circular  in  outline,  and  the  border  usually  contains  one  or 
more  trees  showing  various  stages  of  injury. 

SOUECES  OF   INFECTION 

In  the  treatment  of  any  plant  disease,  a  knowledge  of  the  source 
of  infection  is  important  in  order  that  the  disease  may  be  stopped,  if 
possible,  before  it  attacks  plants  under  cultivation.  Armillaria  mellea  is 
found  on  many  native  species,  including  the  oak,  willow  and  madrono. 
The  indigenous  oak  trees  probably  form  the  chief  source  of  infection, 
but  it  is  not  known  whether  all  oaks  carry  the  disease. 

It  is  not  difficult  to  find,  in  orchards  which  have  been  long  owned 
by  one  family,  authentic  cases  where  the  disease  has  developed  in  areas 
from  which  oak  trees  had  been  removed  many  years  before.    Oak  roots 


CiRC.  289] 


OAK    FUNGUS    IN    ORCHARD    TREES 


decay  very  slowly  and  may  remain  in  the  soil  twenty  or  thirty  years 
after  the  tree  has  been  cut  down.  It  seems  as  if  the  disease  attacks  the 
roots  of  the  fruit  trees  only  when  they  come  into  contact  with  the 
oak  root  fragments.  Thus,  the  fruit  trees  may  not  be  killed  for  many 
years  after  the  orchard  is  planted.  Apparently  the  pieces  of  oak  roots 
are  a  potential  source  of  infection  until  after  they  are  completely 
decayed.  It  has  also  been  observed  that  many  Armillaria  spots  develop 
in  orchards  planted  along  streams  or  old  water  courses.    The  source  of 


Fig,   1. — Mature  apricot  tree  killed  by  oak  fungus  during  the  growing  season. 


infection  in  these  cases  may  be  the  native  vegetation  along  the  banks 
or  the  fragments  of  roots  carried  down  by  the  flood  waters  and 
deposited  on  the  adjoining  land  and  covered  with  sediment. 

Nursery  trees  may  also  form  a  source  of  infection,  as  the  disease 
has  been  found,  in  a  few  cases,  on  nursery  trees.  It  is  probable  that 
only  a  very  small  proportion  of  trees  are  diseased  as  they  come  from 
the  nursery. 

In  Tasmania,*  Armillaria  has  been  reported  to  have  spread  from 
underground  drains  made  of  wood.  When  tile  was  substituted  for 
the  wood,  the  rate  of  spread  of  the  disease  was  appreciably  diminished. 


*  Bulletin  57.     Root-Eot  of  Fruit  Trees,  by  H.  M.  Xieholls 
Stock  Department,  Tasmania. 


Agricultural  and 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Relative  Susceptihility  of  Species. — Nearly  all  of  the  deciduous 
fruit  trees  grown  in  California  are  susceptible  to  the  disease.  Only 
three  exceptions  have  thus  far  been  discovered.  The  three  species 
w^hose  resistance  seems  to  be  vv^ell  established,  are  the  French  pear, 
Pyrus  communis;  Northern  California  Black  Walnut,  Juglans  cali- 
fornica  hindsii;  and  the  Fig,  Ficus  carica.  Oak  fungus  also  attacks 
raspberries,  blackberries,  and  many  ornamental  shrubs,  and  has  been 
found  on  rhubarb  and  potato  plants.  English  or  Persian  walnuts 
(fig.  2)  and  many  hybrids  between  the  English  and  other  species  are 
not  resistant.  Prunus  davidiana,  recently  introduced  as  a  stock  for 
peaches,  and  pear  trees  on  Japanese  stock,  which  may  include  a  mixture 
of  several  species,  show  more  or  less  susceptibility.  Some  of  the  pear 
root  stocks  used  recently  for  their  resistance  to  pear  blight,  have  not 
been  grown  long  enough  in  districts  infected  with  Armillaria  to 
determine  their  degree  of  resistance. 

Of  the  three  principal  rootstocks  used  for  stone  fruits,  observation 
seems  to  indicate  that  myrobalan  is  the  most  resistant,  surpassing  either 
the  peach  or  the  almond  root.  Some  growers  are  replanting  their 
infected  areas  with  myrobalan  seedlings,  to  be  topworked  later  with  the 
desired  varieties.  None  of  these  plantings  are  as  yet  old  enough  to 
show  decisively  whether  or  not  this  method  is  better  than  the  usual 
practice  of  planting  budded  nursery  trees.  In  some  districts  the 
apricot  root  on  heavy  soil  seems  to  show  a  comparatively  high  degree 
of  resistance,  but  on  sandy  soil,  this  root  is  killed  very  quickly. 
Peaches  and  cherries  are  known  to  be  susceptible. 

Factors  in  the  Bate  of  Spread  of  the  Fungus. — The  kind  of  soil  iti 
which  the  fruit  trees  are  growing  usually  seems  to  exert  little  influence 
on  the  rate  of  spread  of  the  fungus.  The  disease  has  been  found  in 
soils  of  many  types,  ranging  from  light  sand  to  heavy  clay  and  adobe, 
but,  dry,  gravelly  soils  and  the  sandy  sediment  soils  often  found  along 
creek  beds  seems  to  show  a  somewhat  more  rapid  spread  of  the  disease 
than  do  the  heavy  clay  types. 

In  some  parts  of  the  state,  there  is  an  impression  among  growers 
that  irrigation  tends  to  increase  the  rate  of  spread  of  the  disease,  but 
this  belief  has  not,  as  yet,  been  substantiated.  Irrigation  may  be  a 
means  of  causing  the  disease  to  die  out  by  hastening  the  decay  of 
infected  roots.  This,  if  true,  would  be  a  means  of  quickly  making  an 
infected  piece  of  soil  safe  for  planting.  The  rate  of  spread  of  the 
disease  shows  great  variation  in  different  regions.  The  loss  may  range 
from  one  or  two  to  forty  or  fifty  trees  a  year.  Where  the  annual  losses 
are  large  it  appears  that  several  diseased  spots  have  coalesced  to  form 


CiRC. 


OAK    FUNGUS    IN    ORCHARD    TREES 


a  single  large  area,  covering  sometimes  several  acres.  Limited  observa- 
tions seem  to  show  that  with  prunes  and  apricots  in  adobe  soil,  the  rate 
of  spread  is  considerably  slower  than  where  these  fruits  are  on  gravelly 
or  loamy  soil. 

The  vigor  of  the  individual  tree  does  not  seem  to  have  any  effect 
on  its  resistance  to  the  disease.  Young  and  vigorous  trees  are  as  liable 
to  attack  as  old  ones.    With  old  trees,  the  presence  of  the  disease  may 


Fig.  2. — Walnut  tree  on  English  walnut  root  killed  by  oak  fungus. 


be  suspected  for  a  year  or  more  before  death  occurs,  but  young  trees 
die  very  quickly  after  the  first  indications  are  given  by  the  drying  and 
falling  off  of  the  leaves. 

The  belief  has  long  been  held  among  growers  that  so  long  as  its 
native  host  is  alive,  the  fungus  does  not  leave  it  to  attack  fruit  trees. 
While  this  contention  may  be  difficult  to  prove,  it  is  an  interesting  fact 
that  many  examples  have  been  found  of  prune  and  apricot  trees  grow- 
ing for  years  in  close  proximity  to  oak  trees  without  contracting  the 


b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

disease.  There  is  some  evidence  to  show  that  Armillaria  exists  in  an 
oak  tree  but  does  not  kill  it.  While  the  oak  tree  is  living,  the  fungus 
is  apparently  unable  to  penetrate  to  the  cambium  layer.  After  the 
death  of  the  host  the  disease  spreads  throughout  the  dead  or  dying 
roots.  In  the  case  of  fruit  trees,  the  fungus  is  apparently  able  to 
penetrate  to  the  cambium  immediately. 

History  of  a  Typical  Orcliard  Infected  with  Armillaria. — A  strik- 
ing example  of  how  oak  fungus  spreads  is  shown  in  the  accompanying 
map  of  an  orchard  in  Santa  Clara  County  (fig.  3).  The  part  of  the 
orchard  shown  on  the  map  originally  contained  1297  prune  and  apricot 
trees  planted  in  1894  on  the  square  system,  22  feet  apart.  French 
prunes,  part  of  which  were  grafted  on  myrobalan  and  part  on  almond 
root,  made  up  the  majority  of  the  planting.  The  apricots  were  top- 
worked  to  Sugar  prunes  when  seven  years  old.  It  is  interesting  to  note 
that  these  trees,  as  shown  in  the  northeast  corner  of  the  map,  have 
withstood  the  advance  of  the  disease  fully  as  well  as,  if  not  better  than, 
the  French  variety  on  Myrobalan  and  on  almond  root. 

Losses  first  occurred  when  the  trees  were  five  or  six  years  old,  and 
have  been  continuous  since  that  time.  Where  trees  died  the  vacancies 
were  refilled  with  prune  trees,  but  these  second  plantings  did  not  long 
survive.  Next,  apples  were  tried,  and  although  somewhat  more  resist- 
ant to  the  fungus,  they  were  removed  because  this  fruit  did  not  pay. 
Then,  for  a  time  the  vacant  spaces  were  devoted  to  garden  vegetables 
and  alfalfa.  Finally,  walnuts  were  planted.  Part  of  the  first  planting 
of  walnuts  was  on  English  root.  These  trees  were  killed  after  a  few 
years.  The  remaining  walnut  trees  which  were  grafted  on  the  Cali- 
fornia black  w^alnut  stock  survived  and  at  the  present  time  are  about 
12  or  14  years  old  and  are  bearing  satisfactory  crops. 

Judging  from  the  apparent  age  of  the  replanted  walnut  trees  the 
area  now  infected  with  oak  fungus  started  from  four  or  five  points 
or  sources.  These  original  spots  gr?vv  in  size  and  finally  coalesced  to 
form  the  irregular  shaped  area  shown  within  the  dotted  lines  on  the 
map  (p.  7).  It  seems  that  one  area  began  near  the  lower  southeast 
corner,  where  the  orchard  approaches  the  banks  of  a  creek.  It  is 
probable  that  infection  started  from  the  native  trees  along  the  bank. 
Other  infected  areas  developed  in  various  places  and  gradually  spread 
until  they  came  together  to  form  one  large  diseased  patch.  The  owner 
of  the  orchard  still  remembers  the  approximate  location  of  the  oak 
trees  which  were  cut  down  more  than  30  years  ago.  In  some  cases  the 
location  of  these  oaks  apparently  coincides  with  what  seem  to  have 
been  the  beginning  points  of  the  disease  in  the  orchard. 


Giro.  289" 


OAK    FUNGUS    IN    ORCHARD    TREES 


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Fig.  3. — A  typical  example  of  an  Armillaria-infected  orchard,  and  how  the 
disease  slowly  but  surely  spreads  over  the  whole  area  if  not  checked  during  its 
early  stages.  This  part  of  the  orchard  originally  contained  1297  prune  and 
apricot  trees  planted  in  1894.  Missing  places  are  now  principally  planted  to 
walnut  trees  on  resistant  stocks. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

At  the  present  time  approximately  860  trees  of  the  original  plant- 
ing have  been  killed.  This  amounts  to  a  loss  of  nearly  66  per  cent  in 
23  years.  In  other  words,  the  average  loss  was  about  37  trees  a  year 
on  an  area  of  about  14  acres.  The  economic  loss  resulting  from  the 
death  of  37  mature  prune  trees  each  year,  together  with  the  non- 
productive period  which  must  elapse  before  the  replanted  walnuts 
come  into  bearing  amounts  to  a  considerable  sum. 

A  study  of  this  orchard,  which  is  no  different  from  many  others  in 
various  parts  of  the  state,  is  of  peculiar  interest,  because  of  the  very 
evident  lessons  it  imparts.  It  shows  first,  the  inexorable  progress  of 
the  fungus  when  once  established  in  a  prune  or  apricot  orchard ; 
second,  the  economic  loss  resulting  from  the  death  of  bearing  trees; 
and  third,  the  best  solution  as  yet  found  for  this  problem :  viz.,  replant- 
ing with  disease-resistant  trees  such  as  walnuts  on  California  black 
Avalnut  root. 

METHODS  OF  CONTEOL 

Up  to  the  present  time  no  method  of  treatment  intended  to  control 
this  disease,  after  it  is  discovered,  has  been  effective.  The  solution  of 
the  problem  seems  to  lie  in  lessening  the  losses  by  checking  the  spread 
of  the  fungus.  Isolating  the  diseased  trees  by  digging  trenches  around 
the  diseased  area  or  by  replanting  with  resistant  stocks  after  the  orig- 
inal trees  have  died  will  accomplish  this.  Trenching  around  the 
infected  area  at  a  safe  distance  beyond  the  visible  limits  of  the  fungus 
may  be  expected  to  give  a  reasonable  amount  of  protection  for  the 
remainder  of  the  orchard.  This  method,  however,  is  practicable  only 
when  the  diseased  area  is  relatively  small.  It  is  also  beset  with  danger 
because  diseased  roots  may  be  left  outside  the  barrier. 

In  the  case  of  many  plant  diseases,  one  of  the  principal  methods  of 
control  is  by  pruning  off  diseased  parts  and  by  burning  or  plowing 
under  infected  material.  This  method  is  not  applicable  to  controlling 
a  root  disease  of  a  large  tree.  When  a  diseased  tree  is  dug  out  of  the 
soil,  it  is  not  practicable  to  remove  all  of  the  roots.  The  idea  of 
disinfecting  the  soil  presents  itself  in  this  connection. 

Various  chemicals  have  been  tested  for  this  purpose.  Up  to  the 
present  time,  the  tests  have  not  been  particularly  successful.  Disin- 
fecting the  holes  from  which  diseased  trees  have  been  removed  with 
such  materials  as  copper  sulfate,  formalin,  sodium  cyanide  and  carbon 
bisulfide  has  not  proved  to  be  a  reliable  method  of  permanently  pre- 
venting infection  of  the  replanted  trees.  Neither  has  the  application 
of  hydrated  lime  to  the  soil  around  trees  adjoining  diseased  areas 
proved  to  be  effective  in  preventing  the  spread  of  the  fungus  (fig.  4). 


CiRC.  289] 


OAK    FUNGUS    IN    ORCHARD    TREES 


In  Tasmania,  excellent  results  are  reported  from  the  application 
of  permanganate  of  potash  or  iron  sulfate  on  the  main  roots  of  trees 
infected  with  Armillaria.  Similar  treatments  (fig.  4)  applied  to  trees 
in  California  using  Weed  Killer    (proprietary  arsenic  compound).* 


Fig.  4. —  Partly  diseased  prune  tree  with  main  roots  uncovered  for  treatment 
with  disinfecting  materials.     No  useful  results  obtained. 


permanganate  of  potash/*  iron  sulfate,*  formaldehyde  and  Bordeaux, 
all  failed  to  control  the  disease.     Likewise,  treatments  w^ith  various 

*  Tliese  materials  have  been  used  by  Col.  G.  E.  Stockle  of  Mountain  View 
on  a  c-onimercial  scale  for  several  vcars  without  success. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


chemicals  by  so-called  tree  doctors  have  not  checked  the  spread  of 
the  fungus. 

Barriers. — Armillaria  spreads  underground  from  tree  to  tree  by 
means  of  root-like  fungous  strands  known  as  rhizomorphs.     Healthy 


»^.r 


Fig.  5. — Portion  of  a  narrow  concrete  barrier  built  around  an  oak  fungus 
area  to  prevent  spread  of  the  disease. 


trees  are  thus  infected  from  adjacent  diseased  ones.  Theoretically, 
the  disease  can  be  checked  by  preventing  the  underground  spread  of 
these  rhizomorphs.  Various  methods  to  accomplish  this  purpose  have 
been  suggested  and  carried  out  to  a  limited  extent.     The  chief  idea 


CiRC.  289] 


OAK    FUNGUS   IN    ORCHARD    TREES 


11 


in  this  method  of  control  is  to  dig  around  the  diseased  area  a  trench 
of  sufficient  depth  to  extend  below  the  area  occupied  by  roots.  This 
trench  may  simply  be  refilled  after  cutting  off  all  crossing  roots  and 
later  reopened  for  the  same  purpose ;  or  it  may  be  lined  with  material 


J 


Fig.    6.^J'.c(-;iusr    tills    uiii'    hUiali    infected    iv-;  -    .,.,-..,     ...-    wall,    the 

barrier,  faintly  shown  on  the  right  of  the  photograph,  failed  to  prevent  the 
spread  of  the  fungus.  The  barrier  should  have  been  placed  one  tree  row  farther 
away  from  the  diseased  area. 

like  tar-paper;  or  it  may  have  constructed  in  it  a  narrow  concrete 
(fig.  5)  wall  extending  from  slightly  below  plowing  depth  to  the 
bottom  of  the  trench. 


12 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  chief  objection  to  the  use  of  the  concrete  barrier  is  its  cost. 
The  enclosed  area  is,  therefore,  usually  made  as  small  as  possible. 
The  danger  in  this  practice  lies  in  the  fact  that  although  the  trees 
bordering  the  diseased  area  are  apparently  healthy,  they  may  have  one 


Fig.  7. — Stump  of  English  walnut  tree  killed  by  oak  fungus.  The  graft 
union  was  covered  with  soil  and  the  disease  entered  the  scion  above  the  graft 
union.  The  black  walnut  root  was  not  injured  and  sent  up  several  sprouts 
after  the  top  had  died. 


or  more  infected  roots.  In  this  case,  the  disease  soon  makes  its  appear- 
ance outside  of  the  barrier.  This  has  actually  happened  in  two 
instances  known  to  the  writer.    In  one  case  when  a  tree  outside  of  the 


CiRC.  289]  OAK   FUNGUS   IN    ORCHARD   TREES  13 

barrier  died,  the  source  of  infection  was  traced  to  a  root  which 
extended  to  the  wall,  but  which  was  not  observed  to  be  infected  when 
the  barrier  was  built  (fig.  6).  For  safety  the  barrier  should  be  put 
not  closer  than  between  the  second  and  third  rows  of  healthy  trees 
surrounding  the  diseased  area. 


CONCLUSIONS 

Oak  fungus  is  a  root  disease  attacking  many  common  deciduous 
fruit  trees  and  ornamentals.  All  root  stocks  used  at  the  present  time 
for  stone  fruits  are  more  or  less  susceptible  to  attack.  Apples  are 
usually  considered  highly  resistant,  especially  if  grown  on  Delicious 
stock,  and  the  French  pear  root  is  practically  immune.  The  fig  and 
California  black  walnut  are  also  highly  resistant  to  this  fungus.  If 
the  infected  area  is  limited  in  extent,  as  in  the  case  of  young  orchards 
when  the  disease  is  first  noticed,  it  may  be  possible  to  check  further 
progress  of  the  fungus  by  enclosing  the  diseased  spot  with  a  concrete 
barrier  as  described  in  this  paper.  When  the  diseased  area  is  extensive 
it  should  be  replanted  with  one  or  more  of  the  resistant  species.  In 
replanting  with  either  pears  on  French  root  or  with  walnuts  on  black 
walnut  root,  care  must  be  taken  to  see  that  the  graft  union  (fig.  7)  is 
not  covered  with  soil,  because  cases  have  been  observed  w^here  the 
susceptible  scion  was  attacked  by  the  disease,  while  the  root  Avas  not 
affected. 


STATION  PUBLICATIONS  AVAILABI^E  FOR  FEEE  DISTRIBUTION 


BULLETINS 
No.  No. 

253.   Irrigation   and   Soil   Conditions   in   the  352. 

Sierra  Nevada  Foothills,  California. 

261.  Melaxiima    of    the    Walnut,     "Juglans  353. 

regia."  354. 

262.  Citrus   Diseases  of  Florida   and   Cuba  357. 

Compared  with  Those  of  California. 

263.  Size  Grades  for  Ripe  Olives. 

268.   Growing  and  Grafting  Olive  Seedlings.  358. 

273.   Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain.  359. 

275.  The  Cultivation  of  Belladonna  in  Cali-  361. 

fornia. 

276.  The  Pomegranate.  362. 

277.  Sudan  Grass  363. 

278.  Grain   Sorghums. 

279.  Irrigation  of  Rice  in  California.  364. 

280.  Irrigation  of  Alfalfa  in  the  Sacramento 

Vallev.  366. 

283.   The  Olive  Insects  of  California. 

285.  The  Milk  Goat  in  California.  367. 

286.  Commercial  Fertilizers. 

294.   Bean  Culture  in  California.  368. 

304.  A   Study  of  the  Effects  of  Freezes  on 

Citrus   in   California.  369. 

310.   Plum  Pollination.  370. 

312.  Mariout  Barley.  371. 

313.  Pruning  Young  Deciduous  Fruit  Trees. 

319.   Caprifigs  and  Caprification.  372. 

324.  Storage  of  Perishable  Fruit  at  Freezing 

Temperatures.  374. 

325.  Rice  Irrigation  Measurements  and  Ex- 

periments    in      Sacramento     Valley, 
1914-1919.  375. 

328.   Prune  Growing  in  California. 

331.   Phylloxera-Resistant  Stocks.  376. 

334.  Preliminary  Volume  Tables  for  Second- 

Growth  Redwood.  377. 

335.  Cocoanut    Meal    as    a    Feed    for   Dairy  379. 

Cows  and  Other  Livestock.  380. 

339.  The  Relative  Cost  of  Making  Logs  from 

Small  and  Large  Timber.  381. 

340.  Control  of  the  Pocket  Gopher  in  Cali- 

fornia. 382. 

343.  Cheese  Pests  and  Their  Control. 

344.  Cold  Storage  as  an  Aid  to  the  Market-  383. 

ing  of  Plums. 

346.  Almond  Pollination.  384. 

347.  The  Control  of  Red  Spiders  in  Decidu- 

ous Orchards. 

348.  Pruning  Young  Olive  Trees.  385. 

349.  A    Study    of    Sidedraft    and    Tractor  386. 

Hitches. 

350.  Agriculture  in  Cut-over  Redwood  Lands.  287. 


Further  Experiments  in  Plum  Pollina- 
tion. 

Bovine  Infectious  Abortion. 

Results  of  Rice  Experiments  in   1922. 

A  Self-mixing  Dusting  Mackine  for 
Applying  Dry  Insecticides  and 
Fungicides. 

Black  Measles,  Water  Berries,  and 
Related  Vine  Troubles. 

Fruit  Beverage  Investigations. 

Preliminary  Yield  Tables  for  Second 
Growth  Redwood. 

Dust  and  the  Tractor  Engine. 

The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal  Dusts  for  the  Control  of 
Bunt. 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in  Relation  to  Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing Pickling. 

Comparison  of  Woods  for  Butter  Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and  Large  Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results  of  Rice  Experiments  at  Cor- 
tena,    1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The  Cold  Storage  of  Pears. 

Walnut  Culture  in  California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin  Valley,   California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Succulent  Feeds  and  Alfalfa  Meal 
as  Sourses  of  Vitamin  A  for  Poultry. 

Pollination  of  the  Sweet  Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig  Smut. 


No. 

87 

113 

117 


Alfalfa. 

Correspondence  Courses  in  Agriculture. 

The    Selection    and    Cost    of    a    Small 
Pumping  Plant. 

House  Fumigation. 
129.  The  Control  of  Citrus  Insects. 
136.  Melilotus    indica    as    a    Green-Manure 
Crop  for  California. 

Oidium  or  Powdery  Mildew  of  the  Vine. 

Feeding  and  Management  of  Hogs. 

Some  Observations  on  the  Bulk  Hand- 
ling of  Grain   in  California. 

Irrigation   Practice   in   Growing  Small 
Fruit  in  California. 


127. 


144. 
151. 
152. 

154. 


CIRCULARS 
No. 
155. 
157. 
160. 
161. 
164. 
165. 


Bovine  Tuberculosis. 
Control  of  the  Pear  Scab. 
Lettuce  Growing  in  California. 
Potatoes  in  California. 
Small  Fruit  Culture  in  California. 
Fundamentals   of   Sugar   Beet   Culture 
under  California  Conditions. 

166.  The  County  Farm  Bureau. 

167.  Feeding  Stuffs  of  Minor  Importance. 
170.   Fertilizing  California  Soils  for  the  1918 

Ci'op. 
173.  The    Construction    of    the   Wood-Hoop 

Silo. 
178.  The  Packing  of  Apples  in  California. 


CmCVhARS— (Continued) 


No. 
179. 

184. 
190. 
199. 
202. 

203. 
208. 

209. 
210. 
212. 
214. 

215. 
217. 

220. 
228. 
231. 
232. 

233. 
234. 

235. 

236. 


237. 

238. 
239. 

240. 

241. 

243. 

244. 
245. 
247. 
248. 

249. 
250. 


Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
A  Flock  of  Sheep  on  the  Farm. 
Agriculture  Clubs  in   California. 
Onion  Growing  in  California. 
County   Organizations   for   Rural   Fire 

Control. 
Peat  as  a  Manure  Substitute. 
Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
The  Function  of  the  Farm  Bureau. 
Suggestions  to  the  Settler  in  California. 
Salvaging  Rain-Damaged  Prunes. 
Seed  Treatment  for  the  Prevention  of 

Cereal   Smuts. 
Feeding  Dairy  Cows  in  California. 
Methods   for   Marketing  Vegetables   in 

California. 
Unfermented  Fruit  Juices. 
Vineyard  Irrigation   in  Arid  Climates. 
The  Home  Vineyard. 
Harvesting    and    Handling    California 

Cherries  for  Eastern   Shipment. 
Artificial  Incubation. 
Winter  Injury  to  Young  Walnut  Trees 

during  1921-22. 
Soil  Analysis  and  Soil  and  Plant  Inter- 
relations. 

The  Common  Hawks  and  Owls  of  Cali- 
fornia   from    the    Standpoint    of    the 

Rancher. 
Directions  for  the  Tanning  and  Dress- 

of  Furs. 
The  Apricot  in  California. 
Harvesting  and  Handling  Apricots  and 

Plums  for  Eastern  Shipment. 
Harvesting    and    Handling    Pears    for 

Eastern   Shipment. 
Harvesting  and  Handling  Peaches  for 

Eastern   Shipment. 
Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 
Central  Wire  Bracing  for  Fruit  Trees. 
Vine  Pruning  Systems. 
Colonization  and  Rural  Development. 
Some  Common  Errors  in  Vine  Pruning 

and  Their  Remedies. 
Replacing  Missing  Vines. 
Measurement   of   Irrigation   Water   on 

the  Farm. 


No. 

251.  Recommendations  Concerning  the  Com- 

mon    Diseases     and     Parasites     of 
Poultry  in  California. 

252.  Supports  for  Vines. 

253.  Vineyard  Plans. 

254.  The  Use  of  Artificial  Light  to  Increase 

Winter  Egg  Production. 

255.  Leguminous   Plants  as  Organic  Fertil- 

izer in   California  Agriculture. 

256.  The  Control  of  Wild  Morning  Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning  Deciduous  Fruits. 

259.  Pear  By-products. 

260.  A  Selected  List  of  References  Relating 

to  Irrigation  in  California. 

261.  Sewing  Grain   Sacks. 

262.  Cabbage  Growing  in  California. 

263.  Tomato  Production  in  California. 

264.  Preliminary  Essentials  to  Bovine  Tuber- 

culosis Control. 

265.  Plant  Disease  and  Pest  Control. 

266.  Analyzing  the  Citrus  Orchard  by  Means 

of  Simple  Tree  Records. 

267.  The  Tendency  of  Tractors  to  Rise  in 

Front;  Causes  and  Remedies. 

268.  Inexpensive  Lavor-saving  Poultry  Ap- 

pliances. 

269.  An  Orchard  Brush  Burner. 

270.  A  Farm  Septic  Tank. 

271.  Brooding  Chicks  Artificially. 

272.  California  Farm  Tenancy  and  Methods 

of  Leasing. 

273.  Saving  the  Gophered  Citrus  Tree. 

275.  Marketable        California        Decorative 

Greens. 

276.  Home  Canning. 

277.  Head,   Cane,   and  Cordon   Pruning  of 

Vines. 

278.  Olive  Pickling  in  Mediterranean  Coun- 

tries. 

279.  The  Preparation  and  Refining  of  Olive 

Oil  in  Southern  Europe. 

281.  The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

282.  Prevention  of  Insect  Attack  on  Stored 

Grain. 

283.  Fertilizing  Citrus  Trees  in  California. 

284.  The  Almond  in  California. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


12m-5,'25 


